Bonding of metallic members with alkali metals and alkali metal containing alloys

ABSTRACT

Bonding of copper and copper containing alloys or silver or silver containing alloys to copper or copper alloys or to silver or silver containing alloys through the use of alkali metal or alkali metal containing alloys.

United States Patent Krock et al.

[is] 3,668,758 [451 June 13, 1972 BONDING OF METALLIC MEMBERS WITHALKALI METALS AND ALKALI METAL CONTAINING ALLOYS Inventors: Richard H.Krock, l26 Conant Road, Weston, Mass. 02193; Earl l. Larsen, 9565 CopleyDrive, lndianapolis, 1nd.

Filed: July 8, 1971 Appl. No.: 160,931

Related US. Application Data Continuation-impart of Ser. No. 109,329,Jan. 25, 1971.

[1.8. Cl ..29/ 199, 29/504 Int. Cl. ...B32b 15/16, B32b 15/20 FieldolSearch ..29/19l, 199,504

References Cited UNITED STATES PATENTS Silliman ..29/ l 99 Bredm..29/504 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-J. E.Legru Attorney-Richard H. Childress, et al.

[57] ABSTRACT Bonding of copper and copper containing alloys or silveror silver containing alloys to copper or copper alloys or to silver orsilver containing alloys through the use of alkali metal or alkali metalcontaining alloys.

70 Claims, 6 Drawing Figures PATENTEDJUH 13 I972 SHEET 1 BF 2 Ulhmllilh.

CONCENTRATION GRADIENT INVENTORS EARL I. LARSEN RICHARD H KROCK ATTORNEYPATENTEDJUN 13 I972 SHEET 2 IJF 2 INVENTORS EARL I. LARSEN RICHARD H.KRo'cK ATTORNEY BONDING OF METALLIC MEMBERS WITH ALKALI METALS ANDALKALI METAL CONTAINING ALLOYS This application is acontinuation-in-part of application, Ser. No. 109,329, filed Jan. 25,1971.

In order to bond a copper member to another copper member or to a silvermember in most instances a brazing operation is carried out in order toobtain a soundjoint.

However, there are certain disadvantages to this brazing operation. Inthe first place, the use of many brazing alloys results in the formationof low melting constituents which limit the use of the brazed joint inits elevated temperature applicatron.

Secondly, often the brazed assembly is softened by the annealing effectof the heating during brazing. Thus, the yield strength, tensilestrength and/or hardness of the component members is substantiallyreduced after the brazing operation. This is true whether the hardeninghas been affected by cold working or precipitation hardening.

Thirdly, often times brittle intermetallic compounds are formed betweenthe members or members being brazed and the brazing alloy composition.Thus, the resulting brazed joint is sometimes brittle.

Finally, the brazing operation is not an inexpensive operation. The costof the brazing alloy together with the cost of effecting the heating ofthe brazing alloy with members to be bonded together is a significantcost item. It may show up for instance in the electric bill or the gasbill of the company effecting the brazing.

It therefore is a first object of the present invention to provide amethod of bonding copper or silver containing members to each otherand/or to other copper or silver containing members which avoids thedisadvantages of the conventional brazing techniques.

It is another object of the present invention to bond members togetherwhich does not result in the softening of the members during bonding.

It is another object of the present invention to bond members togetherwith a technique that does not result in the formation of low meltingconstituents at the brazed joint.

It is another object of the present invention to provide a method ofbonding members together in which the brazed joint does not becomebrittle after the brazing operation.

It is another object of the present invention to provide a method ofbonding members together which is less expensive than the conventionalbrazing technique.

Other objects will be apparent from the following description anddrawings.

FIG. I is a top view of an assembly to be bonded together in accordancewith the present invention.

FIG. 2 is a side view of the assembly of FIG. 1 showing the bondingagent of the present invention prior to bonding.

FIG. 3 is a side view of the assembly after bonding.

FIG. 4a is a sectional view through the bonded assembly.

FIG. 4b shows the concentration gradient of lithium at the bondedinterface and in the component members.

FIG. 5 is a photomicrograph at 160x showing the bonded microstructure.

SUMMARY OF THE INVENTION Alkali Metal Materials including sodium, andsodium alloys, potassium and potassium alloys, lithium and lithiumcontaining alloys are utilized to bond copper, copper alloys, silveralloy containing members to other copper, copper alloys, silver and/orsilver alloys at temperatures below 600 C, with or without theapplication of pressure to the members to be bonded together. Whilealkali metals may be used alone, they are preferably utilized in alloyform; for example, alloys of alkali metals and copper and alkali metalsand silver. The preferred material is lithium or a lithium containingalloy. Thus alloys of lithium and magnesium and ternary alloys such ascopper-silver-lithium, copper-lithium-bismuth, silver-lithium-bismuth,silver-lithium-lead and silver-lithium-thallium may be used.

DETAILED DESCRIPTION A copper or copper alloy or silver or silver alloymay be bonded to another copper or copper alloy or silver or silveralloy member in accordance with the present invention. Exemplary coppermembers include oxygen free copper, tough pitch copper and and phospherdeoxidized copper. See for example Copper Development AssociationNumbers 102, I04, 105, l07, 1 l0, 1 I3, 114, 116, 122,and 145.

Exemplary copper alloys include brasses, bronzes, cupronickel( s) andMuntz metal. As is known by those skilled in the art, the zinc contentin such alloys may vary all the way from a fraction of a percent up to50 percent. It is intended to cover such alloys as commercial bronze,jewelry bronze, red brass, low brass, brass, yellow brass, Muntz metal,leaded bronze, aluminum bronze and silicon additive bronzes. ExemplaryCDA numbers for these various materials include Numbers 220, 226, 230,240, 260, 268, 270, 280, 3M, 330, 340, 360, 365-368, 614, 619, 638 and639.

Additionally, copper alloys containing hardening elements such ascobalt, nickel, zirconium, beryllium, chromium, may be utilized.Generally, chromium may be present in an amount from 0.1 to l.5%,beryllium in an amount 0.3 to about 2.5%, cobalt in an amount from about0.5 to 3% and nickel in an amount 0.5 to 3%. Additionally, the siliconmay be utilized for example in an amount from about 2 to 8%, manganeseup to 15%, aluminum in an amount of about 2 to l0% and tin in an amountfrom about 5 to 15%. Exemplary CDA numbers for these type of materialsinclude numbers l50, 172, 182, 405, 422, 425, 510 and 52 I. It will beapparent from the foregoing that the process of the invention may beapplied to all or nearly all of the currently available copper basedmaterials.

Additionally, refractory metal composites of tungsten and/or molybdenumhaving infiltrated therein copper and/or silver or silver or copperalloys may be bonded according to the present invention. Preferably therefractory metal content is at least 30 percent by weight, with orwithout minor amounts of additives.

Additionally, silver and silver base alloys may be bonded. For example,silver-cadmium, silver-copper and silver-nickel and silver-lead alloysmay be used. Cadmium is generally alloyed with silver in an amount up to25 percent. Silver and copper compositions may be utilized in anyamount, as may silver and nickel alloys. Lead is generally added insilver alloys in an amount not greater than about 15 percent.

With respect to the bonding agent, alkali metals may be used alone oralkali metals containing small amounts of additives may be utilized. Asknown by those familiar with alkali metals, particularly sodium,potassium and lithium and many alkali metal containing materials arevery difficult to handle. They react very rapidly with water, nitrogen,hydrogen, oxygen and other chemicals. While an alkali metal may beutilized alone if careful work is carried out it is generally easier toutilize the alkali metal in combined or alloy form.

Thus, a preferred embodiment of the present invention is to use analkali metal in alloy form. For example, alloys of alkali metals may beused; such as alloys of sodium and lithium, in all proportions, butpreferably up to about 20 percent by weight sodium, alloys of sodium andpotassium, preferably up to 40 percent by weight potassium, and ternaryalloys of sodium, potassium and lithium, preferably containing at least30 percent by weight lithium. Furthermore, alloys of alkali metals withcopper may be used. For example, copper-lithium alloys may be utilizedin which lithium is present in an amount from about 0.1 to about 6percent by weight. If it is desired to avoid partial melting duringbonding the lithium should be present in an amount from 0.2 to about 2.5percent by weight, and temperatures below the liquidus on thecopper-lithium phase diagram avoided. However, the bonding proceeds morerapidly if partial melting does occur and processing in a dry, inertatmosphere using lithium contents and temperatures such that partialmelting does occur can considerably speed the reaction rate.Copper-sodium alloys may be used with sodium present up to 0.1 percent,preferably not above 0.15 percent. Copperpotassium alloys may be usedwith potassium present up to about 0.75 percent, preferably not aboveabout 0.35 percent. Ternary alloys of copper-lithium-sodium orcopper-lithiumpotassium may be used, the lithium content is preferablythe same as for copper-lithium binary alloys, except that the lithiumcontent is reduced to the extent of the sodium and/or potassium. Thusquaternary alloys of Cu-Li-Na-K may also be used.

If a silver lithium alloy is used the lithium content should be fromabout 4 to about 40 percent by weight. Preferably, however, the amountis about to about 30 percent by weight lithium.

If a silver-sodium alloy is used, again the sodium is preferably notabove about 1 percent, and most preferably not above about I percent,and most preferably not above about 0.5 percent. If a silver-potassiumalloy is used, potassium is preferably not above about 0.75 percent byweight, and most preferably below about 0.35 percent. Ternary andquartemary alloys of silver-lithium-sodium and/or potassium may also beused, with the amount of litium decreased to the extent of the sodiumand/or potassium content.

Preferably, the bonding is carried out at a temperature above 330 C ifavoidance of intermetallic formation is desired.

in the case of ternary alloys such as copper-silver-alkali metal theamount of lithium should not be greater than about 2.5 weight percentlithium. If sodium is used, preferably not above about 1 percent, mostpreferably below about 0.5 percent and if potassium is used itpreferably should not be above about 0.75 percent, most preferably notabove about 0.35 percent by weight. Quarternary and live componentsystems may also be used, with sodium and/or potassium substituting forlithium as desired with regard to alloys of copper and silver alone. Theremainder may be silver and copper in any proportion.

Similarly if a bismuth addition is used, it should be present in anamount up to about 35 percent by weight bismuth, the remainder copperand/or silver, with lithium being present in an amount up to about 35percent by weight. Likewise, in the case of silver-lithium-lead orsilver-lithium-thallium, lithium is present in an amount up to about 35percent by weight with the balance either lead and/or silver in anyproportion. Again sodium and/or potassium may be used instead of, or inaddition to lithium in the same percentage ranges as given above.

The method is carried out by placing alkali metal or alkali metal alloymember between each member to be bonded together. Preferably, the alkalimetal containing member is thin compared to the thickness of the membersto be bonded together. There is generally no advantage in making thealkali metal member thick.

When the alkali metal containing member is in contact with the twomembers to be bonded together, the assembly is heated to a temperatureup to about 600 C. Longer times are required at the lower temperaturesand extremely long times are required at temperatures below 150' C. Atthe higher temperatures a small amount of softening may take place dueto a slight annealing effect in some alloys. However, the process doesbond the members together and avoids the greater softening efi'ect dueto annealing which nonnally occurs during brazing. Brazing temperaturesfor most silver and copper alloys are above 600 C.

Pressure may be applied to the joints to be brazed together, for examplea pressure of l to 50 pounds per square inch may be applied to thejoint. Pressure does enhance diffusion and it therefore some reductionin time required is often observed if pressure is applied to the membersto be bonded. lf sufiicient pressure is utilized to mechanically deformthe lithium containing member so that it at least partially fills atleast some voids in the members to be bonded to facilitate diffusion oflithium across the interface.

The preferred temperature range is from about 330 C to about 500 C. Itis within this temperature range that the least reduction of mechanicalproperties occurs. Reduction in mechanical properties is minimized byreducing either processing time or processing temperature.

It is to be emphasized that the difference in properties is verysignificant, for example, choosing CDA alloy number 102,oxygen-free-copper, the annealing effect may result in a yield strengthof component copper near the joint as low as 10,000 to I 1,000 psi. Whenthis material is work hardened it will have a yield strength of 40,000to 50,000 psi. From another standpoint the annealed material has aRockwell F Scale hardness of 40 to 45 whereas the cold worked materialhas a hardness of to Rockwell F. Ofientimes the material to be bondedtogether is in the hard state prior to the brazing operation and thebrazing operation reduces the strength and hardness considerably.Annealed CDA 220 commercial bronze (10 percent zinc) has an annealedyield strength of 10,000 psi and a hardened yield strength of 54,000psi. Precipitation hardened beryllium-copper has an annealed tensilestrength of 50,000 to 80,000 psi and in a precipitation hardened state atensile strength of I65 to I85 psi.

Silver in the annealed state has a tensile strength of 22,000 psi and acold rolled 50 percent tensile strength of 54,000 psi.

With respect to other properties of the bonded joints, the alkali metaldoes not appreciably reduce the thermal or electrical conductivity ofthe silver or copper members.

The method of heating may be any convenient method. The heat may beapplied by a resistance furnace, a gas fired furnace, an inductionfurnace, or resistance heating may be utilized. The type of heating isentirely within designer choice with due regard to the particularconditions prevailing as to the shape of assembly and availablefurnaces.

The longer the members are maintained at temperature the further thealkali metal diffuses into each of the members until a substantiallyuniform concentration in the bonded article is obtained. Therefore, theconcentration of alkali at any point is lower after additional time attemperature. There is concentration gradient as shown in F l6. 1 in eachof the members to be bonded as one moves a distance away from the joint.Therefore, in those few applications where the small reduction inmelting point due to the presence of alkali could cause problemsextended heating within the indicated temperature range would so greatlydiffuse the alkali that this effect would be essentially non-existent.

Obviously, the process could be carried out continuously by utilizingboats or belts through furnace. In addition to avoiding the reduction instrength and hardness, no intermetallics are formed with lithium bondingin copper members as is often the case with brazing alloy. In the eventthat one or more of the component members is a silver base material,formation of intennetallic compounds can be avoided by carrying out thebonding operation at a temperature above 330 C until the lithium hasdiffused into the silver member to the extent that the maximum lithiumcontent is not above 5 weight percent. Then the assembly may be cooledto room temperature and interrnetallic compound formation will beavoided.

This is one of the reasons why lithium and lithium alloys are thepreferred additions over sodium and/or potassium additions. Also,lithium has greater solid solubility in copper, copper alloys, silverand silver alloys than does either sodium or potassium.

Where it is desired to shape or mechanically reduce the cross sectionalarea of the members to be bonded, the members to be bonded can besimultaneously heated and mechanically worked, for example with heatedrolls, to effect simultaneous mechanical deformation and bonding.

A reduction in heating costs can sometimes be achieved over that wherebrazing alloys are used, because lower temperatures are used.

EXAMPLE I An example of the invention, attention is directed to FIG. l-4of the drawings. in this particular application, it is desired to bond ahardened 95% Ag 4.9 wt w/o copper 0.1% Ni member II to a tough pitchcopper member 12. As is apparent from FIG. 2 a layer of coppercontaining 2 percent lithium, 13 is placed between the members and thenthe assembly is heated to a temperature of 350 C for 6 hours.

After the heating operation the assembly is as shown in FIG. 3. Only asmall bond area 23 remains. The concentration of lithium in the bondedassembly may be as shown in FIG. 4b; the diffusion coefficients oflithium in the respective members determines the concentration gradient.

Tests made of the hardness before and after the bonding operationindicated that there was no substantial reduction in hardness andstrength due to the bonding operation. Obviously, the particularmaterials and geometry are by way of example only.

EXAMPLE I] Two pieces of copper with reasonably flat surfaces wereclamped together with a C-clamp with a 5-mil (0.005 inch) sheet of purelithium separating the copper surfaces. The clamp was tightened tomanual tightness. The assembly was heated for 4 days in an argon dry boxat 200 C.

Upon removal of the clamp the copper surfaces were extremely well bondedto one another and a metallograph section showed the copper grain growthoccurred right across the initial boundaries as shown in FIG. 5indicating excellent bond strength. Immersion in boiling water for 4hours showed no porosity indicating extensive lithium diffusion and goodcorrosion strength of the joint.

EXAMPLE III Two pieces of copper with reasonably flat surfaces wereclamped together with a C-clamp with a 5-mil (0.005 inch) sheet of purelithium separating the copper surfaces. The clamp was tightened tomanual tightness.

The assembly was heated for 1 day in an argon dry box at 300 C.

Upon removal of the clamp the copper surfaces were extremely well bondedto one another and a metallograph section showed the copper grain growthoccurred right across the initial boundaries indicating excellent bondstrength. Immersion in boiling water for 4 hours showed no porosityindicating extensive lithium diffusion and good corrosion strength ofthe joint.

EXAMPLE IV Two pieces of copper with reasonably flat surfaces wereclamped together with a C-clamp with a S-rnil (0.005 inch) sheet of purelithium separating the copper surfaces. The clamp was tightened tomanual tightness.

The assembly was heated for 2 hours in an argon dry box at 350 C.

Upon removal of the clamp the copper surfaces were extremely well bondedto one another and a metallograph section showed the copper grain growthoccurred right across the initial boundaries indicating excellent bondstrength. Immersion in boiling water for 4 hours showed no porosityindicating extensive lithium diffusion and good corrosion strength ofthe joint.

EXAMPLE V Two pieces of copper with reasonably flat surfaces wereclamped together with a C-clarnp with a S-miI (0.005 inch) sliver ofpure lithium separating the copper surfaces. The clamp was tightened tomanual tightness.

The assembly was heated for 4 days in an argon dry box at 200" C butwith a Cu-4 w/o Li alloy as the bonding spacer.

Upon removal of the clamp the copper surfaces were extremely well bondedto one another and a metallograph section showed the copper grain growthoccurred right across the initial boundaries indicating excellent bondstrength. Immersion in boiling water for 4 hours showed no porosityindicating extensive lithium difl'usion and good corrodon strength ofthe joint.

Althoughthisworkwasslsocaniedoutinsdryboxitisbelieved that the reducedlithium content reduced the smceptability to oxygen contamination.relaxing the conditions which must bemet inthedry box.

EXAMPLEVI The bonding of silver to copper with lithium was carried outby placing a S-mil lithium sheet between a Hock of silver and a block ofcopper and securing the entire assembly in a C- clamp.

Heating was carried out in an argon dry box for 2 days at 200' Cfollowed by cooling to room temperature.

The resultant joint was of good quality with growth occurring across thebond area.

EXAMPLE VII The bonding of silver to copper with lithium was carried outby placing a S-mil lithium sheet between a block of silver and a blockof copper and securing the entire assembly in a C clamp.

Heating was carried out in an argon dry box for 2 hours at 400 Cfollowed by cooling to room temperature.

The resultant joint was of good quality with growth occurring across thebond area.

EXAMPLE VIII The bonding of copper to silver was carried out by placinga Cu-4 w/o Li sheet 5 mils thick between a surface of copper and asurface of silver, fastening the assembly with a C-clamp and heating theentire assembly in an argon dry box to 350 C and maintaining temperaturefond days.

Bond quality was good with pains growing across the bonded area. i

EXAMPLE IX The bonding of copper to silver was carried out by placing aCu-4 w/o Li sheet 5 mils thick between a surface of copper and a surfaceof silver, fastening the auembly with a C-clamp and heating the entireassembly in an argon dry box to 400 C and maintaining temperature for 2hours.

Bond quality was good with grains growing across the bonded area.

EXAMPLE X Examples 1-3 were repeated but the composition of the brazingmaterial was 72.5 Ag26.4 Cu-l .l Li.

Similar results were obtained.

We claim:

I. A method of bonding a first member to a second member, said firstmember and said second member being made from a material selected fromthe group consisting of copper. copper alloys, silver and silver alloyscomprising placing between the members to be bonded together an alkalimetal containing material and heating the assembly to a temperature offrom up to about 600' C for a time sufficient to bond the memberstogether.

2. A method according to claim 1 wherein said first member is a coppermember.

3. A method according to claim I wherein said first member is a copperalloy.

4. A method according to claim I wherein said first member is a silvermember.

5. A method according to claim 1 wherein said first member is a silveralloy.

6. A method according to claim I wherein said first member is arefractory base composite containing a member selected from the groupconsisting of copper and silver.

7. A method according to claim I wherein said second member is arefractory base composite containing a member selected from the groupconsisting of copper and silver.

8. A method according to claim 1 wherein said second member is a coppermember.

9. A method according to claim 1 wherein said second member is a copperalloy.

10. A method according to claim I wherein said second member is a silvermember.

11. A method according to claim 1 wherein said second member is a silveralloy.

12. A method according to claim 1 wherein said alkali metal containingmaterial is selected from lithium, sodium and potassium.

13. A method according to claim 12 wherein said alkali metal containingmaterial is an alkali metal layer.

14. A method according to claim 12 wherein said alkali metal containingmaterial is an alkali metal alloy.

15. A method according to claim 14 wherein an alloy is an alloy oflithium and a metal selected from sodium and potassi- 16. A methodaccording to claim 14 wherein said alloy is a lithium alloy.

17. A method according to claim 14 wherein said lithium alloy is analloy of alkali metal and copper.

18. A method according to claim 14 wherein said alloy is an alloy oialkali metal and silver.

19. A method according to claim 12 wherein said lithium alloy is analloy of magnesium and lithium.

20. A method according to claim 14 wherein said alloy contains at leastthree elements.

21. A method according to claim 20 wherein said alloy is asilver-copper-lithium containing alloy.

22. A method according to claim 20 wherein said alloy is acopper-lithium-bismuth containing alloy.

23. A method according to claim 20 wherein said alloy is asilver-lithium-bismuth containing alloy.

24. A method according to claim 20 wherein said alloy is asilver-lithium-thallium containing alloy.

25. A method according to claim 20 wherein said alloy is asilver-lithium-lead containing alloy.

26. A method according to claim 1 wherein the assembly is heated to atemperature from 330' to 500 C.

27. A method according to claim l7 wherein said copper alloy containsfrom 0.] to 6 percent lithium.

28. A method according to claim 27 wherein said copperlithium alloycontains from 0. l 2 to 2.5 percent lithium.

29. A method according to claim 18 wherein said silver alloy containsfrom about 4 to 40 percent by weight lithium.

30. A method according to claim 29 wherein said lithium content is fromto 30 percent by weight.

31. A method according to claim 17 wherein said alloy is copper-sodiumalloy.

32. A method according to claim 31 wherein said alloy contains up toabout i percent sodium.

33. A method according to claim 14 wherein said alloy is a copperpotassium alloy.

34. A method according to claim 33 wherein said alloy con tains up toabout 0.75 percent potassium.

35. A method according to claim 33 wherein said alloy contains up toabout 0.35 percent potassium.

36. A method according to claim 18 wherein said alloy is asilver-potassium alloy.

37. A method according to claim 36 wherein the amount of potassium is upto about 0.75 percent.

38. A method according to claim 37 wherein the amount of potassium is upto about 0.35 percent.

39. A method according to claim 18 wherein said alloy is a silver-sodiumalloy.

40. A method according to claim 39 wherein the sodium is up to about 1percent by weight.

41. A method according to claim 40 wherein the sodium is up to about 0.5percent by weight.

42. A method according to claim 20 wherein said alloy is acopper-lithium-sodium containing alloy.

43. A method according to claim 20 wherein said alloy is a cr-lithiumtaining rAmethod ac b orcln g a clalm trirersinsaidalloyisssilver-lithium-sodium containing alloy.

45.Amethodsccordingtoclaim20whereinsaidalloyisssilver-litltium-potassium containing alloy.

46.Amethodaccordingtoclaim 21 whereinssidslloyslso contairu at least onealkali metal selected from sodium and potassium.

47. Amethodaccordingtoclaimfiwhereinsaidsiloycon-48.Analkalimetalbondedarticiecomprisingsfirst member selected from thegroup consisting of silver, silverslloys,copperandcopperalloysbondedtoasecondmember selected from thegroup consisting of copper, copper alloys, silver and silver alloys, theinterface between said bonded members defining a bonded joint, therebeing a concentration gradient of alkali metal from said interface intosaid first and second members with a maximum of said concentrationgradient being at said interface.

49. An article according to claim 48 wherein said first member is acopper member.

50. An article according to claim 48 wherein said first member is acopper alloy.

51. An article according to claim 48 wherein said first member is asilver member.

52. An article according to claim 48 wherein said first member is asilver alloy.

53. An article according to claim 48 wherein said second member is acopper member.

54. An article according to claim 48 wherein said second member is acopper alloy.

55. An article according to claim 48 wherein said second member is asilver member.

56. An article according to claim 48 wherein said second member is asilver alloy.

57. An article according to claim 54 wherein said copper alloy isselected from the group consisting of brasses, bronzes andcupro-nickels.

58. An article according to claim 50 wherein said copper alloy isselected from the group consisting of brasses, bronzes andcupro-nickels.

59. An article according to claim 52 wherein said silver member is analloy of a member selected from cadmium, copper, nickel and lead.

60. An article according to claim 59 wherein the lithium constitutes notabove 40 percent by weight when at least one of the bonded components isa silver member.

61. An article according to claim 59 wherein the maximum concentrationof lithium is not more than 3 percent when the assembly is made ofcopper or copper alloys.

62. An article according to claim 54 wherein the copper alloy containsan additive selected from the group consisting of chromium, beryllium,cobalt, nickel, silicon, aluminum, tin, and manganese.

63. An article according to claim 54 wherein the copper alloy containsan additive selected from the group consisting of chromium, beryllium,cobalt, nickel, silicon, aluminum, tin, and manganese.

64. An article according to claim 48 wherein the alkali metal is atleast one metal selected from lithium, sodium, potassium.

65. An article according to claim 64 wherein the article containslithium.

66. An article according to claim 65 wherein the article also contains ametal selected from sodium and potassium.

67. An article according to claim 66 wherein said article contains bothsodium and potassium.

68. An article according to claim 48 wherein said article containssodium.

69. An article according to claim 48 wherein said article containspotassium.

70. An article according to claim 69 wherein said article containspotassium.

l i Q i

2. A method according to claim 1 wherein said first member is a coppermember.
 3. A method according to claim 1 wherein said first member is acopper alloy.
 4. A method according to claim 1 wherein said first memberis a silver member.
 5. A method according to claim 1 wherein said firstmember is a silver alloy.
 6. A method according to claim 1 wherein saidfirst member is a refractory base composite containing a member selectedfrom the group consisting of copper and silver.
 7. A method according toclaim 1 wherein said second member is a refractory base compositecontaining a member selected from the group consisting of copper andsilver.
 8. A method according to claim 1 wherein said second member is acopper member.
 9. A method according to claim 1 wherein said secondmember is a copper alloy.
 10. A method according to claim 1 wherein saidsecond member is a silver member.
 11. A method according to claim 1wherein said second member is a silver alloy.
 12. A method according toclaim 1 wherein said alkali metal containing material is selected fromlithium, sodium and potassium.
 13. A method according to claim 12wherein said alkali metal containing material is an alkali metal layer.14. A method according to claim 12 wherein said alkali metal containingmaterial is an alkali metal alloy.
 15. A method according to claim 14wherein an alloy is an alloy of lithium and a metal selected from sodiumand potassium.
 16. A method according to claim 14 wherein said alloy isa lithium alloy.
 17. A method according to claim 14 wherein said lithiumalloy is an alloy of alkali metal and copper.
 18. A method according toclaim 14 wherein said alloy is an alloy of alkali metal and silver. 19.A method according to claim 12 wherein said lithium alloy is an alloy ofmagnesium and lithium.
 20. A method according to claim 14 wherein saidalloy contains at least three elements.
 21. A method according to claim20 wherein said alloy is a silver-copper-lithium containing alloy.
 22. Amethod according to claim 20 wherein said alloy is acopper-lithium-bismuth containing alloy.
 23. A method according to claim20 wherein said alloy is a silver-lithium-bismuth containing alloy. 24.A method according to claim 20 wherein said alloy is asilver-lithium-thallium containing alloy.
 25. A method according toclaim 20 wherein said alloy is a silver-lithium-lead containing alloy.26. A method according to claim 1 wherein the assembly is heated to atemperature from 330* to 500* C.
 27. A method according to claim 17wherein said copper alloy contains from 0.1 to 6 percent lithium.
 28. Amethod according to claim 27 wherein said copper-lithium alloy containsfrom 0.12 to 2.5 percent lithium.
 29. A method according to claim 18wherein said silver alloy contains from about 4 to 40 percent by weightlithium.
 30. A method according to claim 29 wherein said lithium contentis from 10 to 30 percent by weight.
 31. A method according to claim 17wherein said alloy is copper-sodium alloy.
 32. A method according toclaim 31 wherein said alloy contains up to about 1 percent sodium.
 33. Amethod according to claim 14 wherein said alloy is a copper potassiumalloy.
 34. A method according to claim 33 wherein said alloy contains upto about 0.75 percent potassium.
 35. A method according to claim 33wherein said alloy contains up to about 0.35 percent potassium.
 36. Amethod according to claim 18 wherein said alloy is a silver-potassiumalloy.
 37. A method according to claim 36 wherein the amount ofpotassium is up to about 0.75 percent.
 38. A method according to claim37 wherein the amount of potassium is up to about 0.35 percent.
 39. Amethod accoRding to claim 18 wherein said alloy is a silver-sodiumalloy.
 40. A method according to claim 39 wherein the sodium is up toabout 1 percent by weight.
 41. A method according to claim 40 whereinthe sodium is up to about 0.5 percent by weight.
 42. A method accordingto claim 20 wherein said alloy is a copper-lithium-sodium containingalloy.
 43. A method according to claim 20 wherein said alloy is acopper-lithium-potassium containing alloy.
 44. A method according toclaim 20 wherein said alloy is a silver-lithium-sodium containing alloy.45. A method according to claim 20 wherein said alloy is asilver-lithium-potassium containing alloy.
 46. A method according toclaim 21 wherein said alloy also contains at least one alkali metalselected from sodium and potassium.
 47. A method according to claim 46wherein said alloy contains both sodium and potassium.
 48. An alkalimetal bonded article comprising a first member selected from the groupconsisting of silver, silver alloys, copper and copper alloys bonded toa second member selected from the group consisting of copper, copperalloys, silver and silver alloys, the interface between said bondedmembers defining a bonded joint, there being a concentration gradient ofalkali metal from said interface into said first and second members witha maximum of said concentration gradient being at said interface.
 49. Anarticle according to claim 48 wherein said first member is a coppermember.
 50. An article according to claim 48 wherein said first memberis a copper alloy.
 51. An article according to claim 48 wherein saidfirst member is a silver member.
 52. An article according to claim 48wherein said first member is a silver alloy.
 53. An article according toclaim 48 wherein said second member is a copper member.
 54. An articleaccording to claim 48 wherein said second member is a copper alloy. 55.An article according to claim 48 wherein said second member is a silvermember.
 56. An article according to claim 48 wherein said second memberis a silver alloy.
 57. An article according to claim 54 wherein saidcopper alloy is selected from the group consisting of brasses, bronzesand cupro-nickels.
 58. An article according to claim 50 wherein saidcopper alloy is selected from the group consisting of brasses, bronzesand cupro-nickels.
 59. An article according to claim 52 wherein saidsilver member is an alloy of a member selected from cadmium, copper,nickel and lead.
 60. An article according to claim 59 wherein thelithium constitutes not above 40 percent by weight when at least one ofthe bonded components is a silver member.
 61. An article according toclaim 59 wherein the maximum concentration of lithium is not more than 3percent when the assembly is made of copper or copper alloys.
 62. Anarticle according to claim 54 wherein the copper alloy contains anadditive selected from the group consisting of chromium, beryllium,cobalt, nickel, silicon, aluminum, tin, and manganese.
 63. An articleaccording to claim 54 wherein the copper alloy contains an additiveselected from the group consisting of chromium, beryllium, cobalt,nickel, silicon, aluminum, tin, and manganese.
 64. An article accordingto claim 48 wherein the alkali metal is at least one metal selected fromlithium, sodium, potassium.
 65. An article according to claim 64 whereinthe article contains lithium.
 66. An article according to claim 65wherein the article also contains a metal selected from sodium andpotassium.
 67. An article according to claim 66 wherein said articlecontains both sodium and potassium.
 68. An article according to claim 48wherein said article contains sodium.
 69. An article according to claim48 wherein said article contains potassium.
 70. An article according toclaim 69 wherein said article contains potassium.